High frequency signaling system



H. A. AFFEL.

HIGH FREQUENCY SIGNALING SYSTEM Original Filed Deo. l5. 1922 to [ar/felElayne/icy) Power Generator' Load z'lfzdactamce.

INVENTOR Power Generally' Power-Zine Carrier,

ATTORNEY Pateted Oct.. 3,1933 e 1,928,610 HIGH FREQUENCY SIGNALINGSYSTEM Herman A.`Aiel, Maplewood, N. J., assigner to American Telephoneand Telegraph Company, a corporation of New York Original applicationDecember 15, 1922, Serial No. 607,193, Patent No. 1,615,896, February 1,1927. Divided and this application December 24, 1925. Serial N o. 77,605

'z claims. (ci. 17u-352) This invention relates to high frequencysignaling systems, and particularly to means for rendering such systemshighly selective.

This isa division of the applicants copending application Serial No.607,193 filed December 15, 1922, which issued as Patent No. 1,615,896 onFebruary 1, 1927.

In the development of the radio art, various methods and means have beendisclosed, the object of which has been to increase the selectivity ofsignaling circuits. The best known of all methods consisted in sharplytuning the circuit so as to make it highly selectiveof the frequenciesthat it was desired to transmit or receive.

It is one of the objects of this invention to obtain greater selectivityin the antenna circuits themselves by employing long loop circuits andbytransposing the conductors of the loop, which may be either acompletely metallic circuit, or

a partly metallic and partly grounded circuit, at intervals properlyrelated to the wave length intended to be received. y

Other objects of this invention .will be apparent from the followingdescription, when read in connection with the attached drawing of whichFig. 1 shows schematically the application of the invention to a systemfor transmitting carrier frequency signals over a power transmissionline simultaneously with the transmission thereover of the powercurrent; Fig. 2 is a plan view of a transmission line showing therelative position of the power line and the antenna; and Figs. 3, 3a, 3band 4 illustrate the principle underlying the invention.

InFig. 1 the power transmission line 1 has con- Y l nected therewith apower generator 2 which would normally be ofthe low frequency type andat the distant end a load 3. Bridged across the line 1 near theright-hand end is an inductance 4 and a condenser 5, and similarly, nearthe left-hand end an inductance 6 and a condenser '7, the purpose of thesaid inductances and condensers being to provide, in effect, a lowimpedance short circuit of the line forthe signaling carrierfrequencies. Associated with this tuned section of the line near theleft-hand end is a loop 8 having inserted therein a transposition 1 0which in combination with the tuned circuit, if the loop is of theproper length, that is, one-half of the carrier wave length A, and thetransposition is located at the midpoint of the said loop, will renderthe transmission between the said loop circuit and the linehighlyselective to the carrier frequency and discriminatory to the powerfrequency. The loop 8 is terminated in a resistance 18 equal to thecharacteristic impedance of the loop, for the purthe end of the loopwhich might negative the desirable effects that the loop is capable ofpropose of avoiding undesirable reection effects at f ducing. Bridgedacross the sides of the loop are 160 the drainage coils 12 and 12connected to ground by conductor 1'3, the object of which is to preventcurrents set up by potentials induced between the loop circuit andground from affecting the carrier apparatus connected with the loopcircuit. This carrier apparatus which is designated 16 may be of anywell-known type having means for detecting the signal superimposed onthe carrier wave, and need not be particularly' described here. A

similar loop 9 whose length also is and which has a transposition 11 atits midpoint, is inductively related with the transmission line 1 at theother end of the tuned 'section of the said line.

This loop circuit has bridged across its sides `the coils 14 and 14'which are connected to ground by conductor 15. Carrier apparatus 17,preferlably similar to 16, is connected with the said loop `circuit fortransmitting and receiving purposes.'

The principle underlying this invention is briefly as follows: If thecarrier apparatus'l is transmitting signals, the current set up in thetransmission line 1 by the antenna 8 will be partly dueto the mutualinductive relations between those circuits and partly due to thecapacity unbalance relationships. The voltage in line 1 due to themutual inductive effect manifests itself as a voltage induced seriallyin the line wires; the voltage due to the unbalance capacity effectmanifests itself as a voltage across line wires. There are, furthermore,phase differences between those two voltages and also phase effects thatdepend upon the relation between the length of the line circuits and thefrequencies employed. The resultant voltage is therefore a combinationof those effects. The current wave resulting therefrom will tend totravel toward the terminals ofthe linel. It has been found both bytheory and practice that the current wave traveling toward the distantterminal of the line 1 tends to become substantially zero because themagnetic and capacitative effects referred to tend to oppose each otherwith little or no resultant effect. In the absence of the low impedanceshort circuit for the carrier frequencies comprising the inductances andcondensers bridged across the line 1, the current wave would also tendto travel in the direction toward the generator 2. Furthermore, thecurrent wave that flows in the transmission line toward the generator 2is much larger than Cil the part that owed toward the distant terminalsince the conditions governing wave propagation and phase change aredifferent in the two directions. That current would be absorbed by thepower generator circuit if the latter had an impedance approximatelyequal to the characteristic impedance of the line circuit. I have foundthat this near-end current may be usefully employed in effectingtransmission of signals to the distant terminal. That result is obtainedby using the resonant shunt 6-7 that is tuned to the carrier frequency.That causes a reflection approaching in degree 100 per cent of thecurfent that normally would ow to the generator 2. Furthermore, thetransposing of the loop 8 substantially increases the near-end" currentin the line 1 which, as pointed out, is reflected to the distantterminal. If the loop 8 is one-half of the length of the carrier waveand is transposed at its midpoint, a substantial increase in the nearendcurrent takes place that greatly increases the effectiveness oftransmission of the system.

The physical relation of the loop antenna and the power line is shown,in simple form in Fig. 2, in which the conductors of the power line 1are supported by insulators on pins at the extremities of the crossarms20 upon the poles 21. The loop antenna 8 comprises the conductors 22supported by insulators on pins near the midpoint of each crossarm.which conductors are parallel to those of the power line. As previouslymentioned, the total length of the loop equals M2, where i is the lengthof the carrier wave, and is transposed at its midpoint, viz, at crossarm20. Bridged across the conductors at their right-hand end is theresistance 18, which may be supported in a housing (not shown) attachedto the crossarm or pole. The left-hand ends of the conductors areconnected by suitable leads to the carrier transmitting and receivingapparatus located at A'the terminal station. Other variations areobvious. The antenna need not be in the same plane as the conductors ofthe power line, since the former may be above or below the latter.

It will be apparent from the foregoing description of the arrangementshown in Fig. 1 that the loop circuits with which the carrier frequencyreceiving and transmitting apparatus is associated and inductivelyrelated with the power line, permit the modulated signals to betransmitted from the loop circuits to the tuned section of the powerline by virtue of the inductive relationship existing between them.These` loop circuits, or short inducing lines, should be transposed insuch manner that the potentials induced by the power energy will tend tobalance out by virtue of the relatively low frequencies and relativelysmall phase change involved, but the carrier frequencies will beefiiciently transferred in both directions between the power lines andthe short inducing lines 8 and 9, due to their considerably greaterphase change.

' Themanner by which those results are accomplished will be clearlyunderstood from the following description when read in connection withFigs. 3, 3a, 3b and 4 that illustrate the basic principles underlyingthe invention.

If we take twol paralleling line circuits in proximity, such as shown inFig. 3 of the drawing, and apply to circuit A a voltage from generatorG, current will be induced in circuit B.v

This current will be partly the result of the mutual inductive relationsbetween the two circuits and partly because of capacity unbalancerelationships, i. e., the capacitance between the wires concerned willbe dissymmetrical, as shown in Fig. 3a, for the wires will not be atequal dis-v tances from one another.v These effects will be true forpractically any disposition of the two pairs with respect to one anotherwith a few exceptions, such as the case, shown in Fig. 3b, where the twopairs are'crossed.

That voltage which is induced in circuit B from circuit A, due to themutual inductive effect, manifests itself as a voltage induced seriallyin the line Wires. That resultant voltage which 'is due to the unbalancecapacity effects, manifests itself as a voltage applied across the linewires. Furthermore, there are phase dif ferences between these twovoltages. There are also phase effects because the line circuits may beof such a length as to represent fractions of or perhaps even many wavelengths for the frequencies concerned. This is particularly true of thehigh frequencies which are used in power line carrier transmission work.The resultant induced voltage and current in the circuit, such as B fromcircuit A, is therefore a combination of these several effects. I t hasbeen noted by theoryand practice that under these conditions, thatcurrent which tends to travel toward terminal 2 of circuit B, or what,in telephone practice, is called a far-end crosstalk, tends to besubstantially zero, because the magnetic and capacitative effectsreferred to above tend to oppose each other with little orno resultanteffect. This is true, even though in circuit A transpositions areapplied, at which points the line Wires of the circuit are crossed.

Therefore, if circuit B is considered as a power line, and circuit A aloop circuit which is erected to parallel the power line B for thepurpose of inducing currents from a power line carrier systern connectedat G, and if the other terminal of the power line carrier system is inthe direction of 2, very little current from the power line carriedsystem will reach the further terminal.

However, the current induced in circuit B from circuit A must not onlybe considered from the standpoint of its far-end effects, as notedabove, but also in the direction backward toward the generator circuit.Under these conditions, the wave propagation and phase change effectsare such that the situation differs from the far-end effect noted above.A much larger near-end induced current or crosstalk exists. This currentwould, however, be absorbed in the power generator circuit itself, ifthe latter had an impedance approximately equal to the characteristicimpedance of the power line circuit., For the purpose of making thisnear-end current ef fective in the carrier transmission, however, .ashort circuit in the form of the resonant circuit R is applied,effective for the carrier frequency, as shown in Fig. 4. Therefore thiscurrent is refiected to a degree approaching 100 per cent, and reversesits direction to be transmitted to the desired terminal 2. Furthermore avery substantial increase in the near-end current induced in circuit Boccurs when the inducing circuit A is transposed at distances which areone-quarter wave length apart for the carrier frequency. In other words,if the carrier frequency employed were 100,000 cycles or 3000 meters,and if the inducing line A were made 1500 meters in length, and if thetransposition point is made in the middle of this inducing line, asubstantial increase in the near-end induced current will take place.This, in turn, by being reected to the im' end 2 will therefore greatlyincrease the ei- /ffectiveness off/*transmission ofthe system. It hasbeen estimated thatthis increase in effecl inducing circuitA in Fig. 4is shown terminated `in a resistance equal to its characteristic im- Apedance `T for Athepurpose zof avoiding undesir- 'able reection effectsatthe end vof the inducing wires which might void the desired effectsnoted above. This Y transposition applied in theV inducing circuit is.effective' because of its/relation to the carrier wave length, not onlyin increasing the inductive effects between the two circuits, but valsobecause the power generating wave length isk so much longer it greatlydecreases the voltage induced in circuit A from the power line itself.

While, as noted above, the theory underlying the inductive effectsbetween two circuits includ-- ing both the magnetic and capacitativecomponents of the induced currents is rather complicated, and notparticularly simple of explanation, especially in the case of far-endeffects where the, two components tend to cancel each other, it is notdimcult to see why the neareend effects are increased by the addition ofa transposition in vthe inducing circuit as noted above. For thispurposeone might consider. the current induced at the near end ofcircuit B, where the short circuit is applied, to be the combinedeffects of currents induced from the two sections of the inducingcircuit a and b, respectively. Iffthe current induced from section a atpoint R.

is regarded as of'unit magnitude and zero phase,

then theaverage current induced from section b will return to point R ata lagging phase of M2 or 180. is because there will be a lag of 90 intransmission from the generator to section b, and 90; more in returningthe same length of circuit oventhe power line. The combined effect atpeint4 Rswill therefore tend to be zero, because of the effect of thecurrents at 180 phase displacement. On the other hand, it is obviousthat ifar transposition is applied at the center of theinducing circuit,that current which is the resultof'induction from section b of theinducingfline `A 'will return in phase with the current induced from a,and therefore the two will add, and the effects will be substantiallyimproved, as noted above.

Although this invention has been described as embodiedfin' a particularform and arrangement of it is to befunderstood that it is capable ofembodiment in fotherpand different forms withinfjthe;I spirit and scopeof the appended claims.

What is claimed is:

1. In a high frequency signaling system, the

g combination with a power transmission circuit of means connectedacrossthe said circuit to provide low impedance paths to a frequency differingfrom the power frequency, loop circuits in inductive relation with thesaid transmission circuit and transposing means to render the said loopcircuits selective to the said different frequency.

2. In a'high frequency signaling system, the combination with a powertransmission circuit of/'means connected across the said circuit to`,Drovide low impedancepaths to a frequency differing from'the powerfrequency, loop circuits in inductive relation with said transmissioncircuit, the said loop circuits being in length equal to a definitefraction of the length of the Wave of the said different frequency andbeing trans. posed at their midpoints .torender them selective tothesaid'diiferent frequency.

3. In a high frequency signaling system, the combination with atransmission line capable of transmitting a plurality of frequencies ofa shunt across the sides of the said line providing a low impedance pathfor a certain frequency, and a transposed loop coupled with the saidline responsive to the said certain frequency.

4. In a high frequency signaling system, the combination with atransmission line capable of transmitting a plurality of frequencies ofa shunt across the sides of the said line providing a low impedance pathforcertain of said frequencies and a loop coupled with the said line,the said loop being in length equal to one-half that of the Wave of thesaid certain frequency and being effectively transposed at its midpoint.

5. In a high frequency signaling system, the combination with atransmission line capable of transmitting a plurality of frequencies ofshunts across the sides of the said line, providing low the currents ofpower frequency will tend tobalance out in said loop but the carrierfrequencies will be effectively transferred between said line and saidloop and vice versa,vandterminal apparatus connected to thesaid loopresponsive vto the said carrier frequency.

'7. In a high frequency signaling system, the combination with a powertransmission line capable of transmitting currents of a power frequencyand a carrier frequency, of a loop coupled with the said line, the saidloop being in length equal to one-half that of the wave to be set up inthe said loop and also being effectively transposed at its midpoint, andterminal apparatus connected to the said loop responsive to the saidcarrier frequency.

HERMAN A. AFFEL.

